1. Field of the Invention
The present invention relates to a control apparatus for conducting serial communication with a plurality of electronic devices thereby constitutes an electronic control system, and a self-diagnostic method in the electronic control system.
2. Description of the Related Art
Conventionally, a configuration as shown in FIG. 11 is used in various control. In a field so-called mechatronics, for example, a plurality of power devices 1, 2, 3 of No.1 to No.3 are used for driving various actuators by electronic control. Each power device 1, 2, 3 can pass a current to a motor or a solenoid to generate driving force, or pass a current to a heater to generate heat. Such an electronic control system 10 is controlled by a program operation by a CPU 12 of a control apparatus 11. Connections between the control apparatus 11 and the power devices 1, 2, 3 are made through a communication line 13. In case in which each power device 1, 2, 3 drive an actuator by a large current of, for example, several amperes or more, the power devices 1, 2, 3 are placed in the vicinity of the actuator and are separated from the control apparatus 11. The power devices 1, 2, 3 maybe integrated with the control apparatus 11 or placed close to the control apparatus 11, but this causes that each power device 1, 2, 3 is distant from the actuator and a driving output of a large current is sent over a long distance. In case in which connections between the control apparatus 11 and the power devices 1, 2, 3 in a distant position are made through the communication line 13 and data necessary for control is transmitted by serial communication, the number of communication lines 13 can be reduced.
In order to perform control with high reliability by the electronic control system 10 shown in FIG. 11, there may be provided a function of performing self-diagnosis for determining whether or not an abnormal operation is occurring before each power device 1, 2, 3 actually drives and controls the actuator or in a proper timing during the control. For example, in the electronic control system 10 which is mounted in an automobile and performs various control, a self-diagnostic result is sent from each power device 1, 2, 3 to the control apparatus 11 through serial communication and the whole self-diagnosis or operation monitoring of the electronic control system 10 is performed by the control apparatus 11. The electronic control system 10 mounted in an automobile is operated by receiving electric power supply from a power source system of the automobile. At a time of an abnormal drop in power source voltage, a reliable operation cannot be performed. As a measure to this, a low-voltage detection circuit 14 is provided and a preset fail-safe operation is performed when the abnormal drop in power source voltage supplied from a battery 15 is detected.
As shown in FIG. 12, when the power source voltage drops abnormally and becomes less than or equal to a low-voltage detection level set in the low-voltage detection circuit 14 at time t0, the low-voltage detection circuit 14 gives a low-voltage detection signal, which indicates that the power source voltage drops abnormally, to the CPU 12 At this time, if the control apparatus 11 is receiving data about a self-diagnostic result from the power device No.2 through the communication line 13, subsequently, data from the power device No.3 and data from the power device No.1 are sequentially received. Since the data from the power device No.2 is received when the low-voltage detection signal indicates abnormal state, there is a possibility that a self-diagnostic function performs wrong detection. Thus, the data from the power device No.2 is cleared. When the power source voltage recovers to the low-voltage detection level or more at time t1, the low-voltage detection signal changes to indicate a normal state.
JP-A-9-282028 discloses a self-diagnosis about the electronic control system. This prior art discloses an idea for performing a self-diagnosis by varying a power source to determine whether or not an input device such as a sensor has failed.
In the configuration shown in FIG. 11, even when an abnormal drop in power source voltage is detected and data indicating a self-diagnostic result received by serial communication is made invalid during occurrence of abnormality, it takes time to complete sending the data, which may includes wrong detection affected by the power source voltage abnormality and is sent from all the power devices 1, 2, 3, due to a sending delay. Thus, even when the low-voltage detection signal returns from abnormal state to normality state subsequent to time t1, there is a possibility that abnormal data is received in the control apparatus 11, causing harm to self-diagnosis of the electronic control system 10.